1. Field of Invention
The present invention related to a light source that supplies a collimated beam to a system such as a projector.
2. Description of Related Art
Semiconductor light emitting devices such as light emitting diodes (LEDs) are among the most efficient light sources currently available. Material systems currently of interest in the manufacture of high brightness LEDs capable of operation across the visible spectrum include group III-V semiconductors, particularly binary, ternary, and quaternary alloys of gallium, aluminum, indium, and nitrogen, also referred to as III-nitride materials; and binary, ternary, and quaternary alloys of gallium, aluminum, indium, arsenic, and phosphorus. Often III-nitride devices are epitaxially grown on sapphire, silicon carbide, or III-nitride substrates and III-phosphide devices are epitaxially grown on gallium arsenide by metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or other epitaxial techniques. III-V devices include a light emitting or active region sandwiched between an n-type region and a p-type region.
One promising use of semiconductor light emitting devices is as a light source in a projector, in which images on a liquid crystal display (LCD) are magnified and projected. In a common prior art projector, the LCD is illuminated by a metal halide or halogen lamp. The use of such lamps limits the degree to which the size of the light source, and therefore the size of the projector, can be reduced.
FIG. 1 is a perspective view of a prior art projector, described in more detail in U.S. Pat. No. 7,131,735. Light-emitting diodes (LEDs) 103 serving as point light sources are arranged in a planar arrangement facing an end face of a light guide body 102 (an acrylic resin square bar). The diodes are separate from light guide body 102. A liquid-crystal display element 101 is disposed facing the other end face of light guide body 102. Light emitted by the light-emitting end face of the light guide body 102 strikes liquid-crystal display element 101. The image displayed by the liquid-crystal display element 101 is magnified by a projection lens 104 and is projected onto a screen. The light guide body, which is necessary to mix the light from LEDs 103 in order to uniformly illuminate liquid crystal display element 101, makes the projector undesirably bulky.